Photomask having alignment marks

ABSTRACT

A photo mask for detecting misalignment of stepper blades and undesirable pattern array on an wafer comprises: a number of highest limit alignment marks 5 to 8 located in the outside of a field pattern area for forming product dies on the wafer and indicating the highest limits in setting positions of the stepper blades respectively and a number of lowest alignment marks 9,10 and 11 located respectively in three corners of the said outside of the field pattern area and indicating the lowest limits in setting positions of the stepper blades respectively, and forming a predetermined geometrical shape together.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photo mask having alignment marks andmore particularly to a photomask having alignment marks for detectingundesirable location of stepper blades and undesirable mask patternarray on a wafer.

2. Description of the Prior Art

A conventional type of a photomask will be described, in referring toFIG.1.

FIG.1 shows an arrangement view of a photomask in company with stepperblades which consist of top stepper blade 3a, bottom stepper blade 3b,left stepper blade 3c, right stepper blade 3d.

Each stepper blade making a right angle moves left and right towardpattern area 1 and remains the necessary part, that is, pattern area 1,according to a shape of a photomask 12 and cuts off ultraviolet raysfrom the unnecessary part of photo mask.

However, when the stepper blades are inaccurately located because ofinput errors, a photo mask is more open or covered.

So, if a photo mask is more open, an unnecessary pattern and aunintended peripheral area of wafer is exposed and a product die ofwafer is inferior if a photo mask is more covered, a necessary pair ofpattern and wafer is not exposed and a product die of wafer is inferior

Furthermore, the prior art have one or more collateral difficultiesdetecting misalignment of stepper blades and the array of product dieson the wafer when the first pattern is formed,

Accordingly, the object of the present invention is to provide aphotomask having alignment marks for detecting undesirable location ofstepper blades and undesirable mask pattern array on a wafer.

SUMMARY OF THE INVENTION

A photomask having alignment marks for detecting misalignment of thestepper blades according to the present invention is defined by claimswith a specific embodiment shown in the attached drawings. The inventionrelates to a photo mask for detecting misalignment of stepper blades andpattern array comprising: a number of first alignment marks located inthe outside of a field pattern area for forming product dies on thewafer and indicating the highest limits in setting positions of thestepper blades receptively; and a number of second alignment markslocated respectively in three corners of the said outside of the fieldpattern area and indicating the lowest limits in setting position of thestopper blades respectively, and forming a geometrical shape together.

BRIEF DESCRIPTION OF THE DRAWINGS

For understanding of the nature and objects of the invention, referenceshould be had to the following detailed description taken in conjunctionwith the accompanying drawings in which;

FIG.1 illustrates an arrangement view of a typical photomask in companywith stepper blades of a prior art,

FIG.2 illustrates an arrangement view of a photomask having alignmentmarks in company with stepper blades according to an embodiment of thepresent invention.

FIG.3 illustrates a wafers having a geometrical shape of developed lowerlimited alignment marks and product dies.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2A to 2B illustrated the arrangement view of a photomask havingalignment marks in company with stepper blades according to anembodiment of the present invention.

Referring to FIG.2A, a photomask 12 have reticles (2a through 2d) andthe lowest limited alignment masks 5 to 8 and the highest limitedalignment marks 9,10 and 11 for stepper blades 3a through 3d.

Left stepper blade 3c is located between the highest limited alignmentmark 5 and the lowest limited alignment mask 11 and right stepper blade3d is located between the highest limited alignment mark 7 and thelowest limited alignment mark 9 and 10.

Also, top stepper blade 3a is located between the highest limitedalignment mark 6 and the lowest alignment mark 9 and bottom stepperblade 3b is located between the highest limited alignment mark 8 and thelowest limited alignment mark 10 and 11.

the highest limited alignment marks 5 to 8 is formed by a non chromematerial on a photomask 12 in order to find direction. A distancebetween pattern area 1 and the lowest limited alignment mark is5,000-20,000 μm.

A width of the lowest alignment mark line is 5-10 μm, and the lowestalignment marks are formed by a chrome material on a photo mask 12, asshown FIG.2B.

After a photomask is exposed, if the position of stepper blades isnormal, a pattern of the lowest limited alignment mark must be formedand a pattern of the highest limited alignment mark must not be formedon a wafer

FIG.3 shows a wafer having a geometrical shape of the lowest limitedalignment marks and product dies, product dies and connecting shapes ofthe developed lowest limited alignment marks appear on a wafer when maskpattern is developed on a wafer, moving a wafer left and right, up anddown, as shown in FIG. 3.

If the connecting shapes of the lowest limited alignment marks bring todistortion and cutting line, mask pattern array and the location ofstepper blades are mistaken.

Also, the highest limited alignment marks 5 to 8 appear on a wafer incase that stepper blades is more open, as show in FIG.3. The photo maskaccording to the present invention has the following benefits incontrast with the prior art:

1) In case the first patterns are formed, a misalignment of patternarray is easily detected on a wafer in which the standard vernier is notformed.

2) the setting position of stepper blades is accurately located andfound

3) the photomask pattern process can be simply accomplished and amistake of photomask pattern process can be decreased.

4) the productivity of semiconductor chip is increased.

What is claimed is:
 1. A photomask for detecting misalignment of stepperblades and an undesirable pattern array on a wafer, comprising:a numberof highest limit alignment marks located in the outside of a fieldpattern area and indicating the highest limits in setting positions ofthe stepper blades receptively; and a number of lowest limit alignmentmarks located respectively in three corners of the said outside of thefield pattern area and indicating the lowest limits in setting positionsof the stepper blades respectively, and forming a predeterminedgeometrical shape together.
 2. A photomask according to claim 1, whereinthe first alignment marks are formed in the shape of a letter in orderto indicate top, bottom, left and right directions respectively.